Origin of paired fins: insights from exceptionally preserved jawless fish fossils

Paired appendages represent a key innovation of vertebrates: their origins set the stage for new modes of swimming and the eventual transition from water to land. However, the origins of fins and their supporting skeletal girdles remains a mystery and one of the “holy grails” of vertebrate evolution. We have uncovered new evidence regarding key theory on the origin of the shoulder girdle: that it derived from an ancestral gill arch. However, this theory so far lacks support from the fossil record. The goal of this project is to investigate the skull and shoulder anatomy of key ‘transitional’ jawless fishes near the origin of jawed vertebrates, known as osteostracans to test our new hypothesis. We will use synchrotron tomography to illuminate the structure of the braincase, blood supply, and innervation of exceptionally preserved osteostracan fossils. These will provide insights into the relationship between the gill skeleton and the origin of the shoulder and paired fins.